In one aspect, the invention relates to downhole tool. In another aspect, the invention relates to securing a downhole tool in a borehole. In yet another aspect, the invention relates to fixtures for a downhole tool.
Where seismic data is obtained from a tool positioned downhole, the best results are obtained when the tool is tightly secured to the formation. This is because measurements of seismic wave motion are distorted by a loose tool and do not provide the operator with signals representative of the seismic waves in the surrounding formation. The weight of downhole tools (from 50 up to several hundred pounds) is known to cause difficulty in securing the tool to the earth. It would be very desirable to provide a downhole tool which can be firmly secured downhole in a highly reliable manner.
Another problem encountered in data measurement with downhole tools is that boreholes vary in diameter. For example, drill bits may be used to bore a hole having a diameter ranging from a few to many inches in diameter. Also, the earth formation may shift to partly pinch off the bore downhole or the borehole may become eroded to a locally larger diameter. Thus the diameter of the bore in the same hole may vary. A downhole tool which can be easily adapted to accommodate changing or changed borehole diameters would be very desirable.
Distortion between seismic waves and the recording made by a downhole device can also occur at the interface between the device and the borehole wall due to a poor plant. In certain prior art devices, the downhole tool was locked to the hole wall by an arm providing securing forces in a single plane. Distortion in the measurement of borehole wall motion in directions outside of the locking plane was common. A downhole tool positioned by locking forces in more than one plane is clearly desirable.